Porous Ceramic Sintered Body

ABSTRACT

The present invention provides a porous ceramic sintered body suitable for plant growth and with a high cooling effect. 
     The present invention relates to a porous ceramic sintered body including a pore volume, which is the total volume of pores with a diameter of 3 nm to 360 μm, of 0.2 cm 3 /g or larger and including a micropore volume ratio of 30% by volume or more, in which the micropore volume ratio equals to the total volume of pores with a diameter equal to or greater than 0.01 μm and less than 1 μm divided by the pore volume.

TECHNICAL FIELD

The present invention relates to a porous ceramic sintered body.

Priority is claimed on Japanese Patent Application No. 2010-208458,filed Sep. 16, 2010, the content of which is incorporated herein byreference.

BACKGROUND ART

Generally, a porous ceramic sintered body is used for an insulatingrefractory material, a water purification material, a humidityconditioning material, a volatile organic compound (VOC) adsorptionmaterial or the like. As a structure of this porous ceramic sinteredbody, a closed-cell foam type structure, a lattice type structure, anaggregate type structure, a structure with minute cracked pores, astructure with consecutive through holes, and the like are exemplaryexamples and the structure is selected depending on the use.

A porous ceramic sintered body having a lattice type structure in whichceramic compositions are injected into air holes of urethane foam resinto fill the same and then resin components are decomposed and theresultant is sintered has been known.

A porous ceramic sintered body having an aggregate type structure inwhich voids of aggregate of elementary particles in a composition areused as air holes has been known.

A porous ceramic sintered body having a closed-cell foam type structurein which air holes are generated by high temperature decomposingvolatile components in a composition in a calcination step has beenknown.

A porous ceramic sintered body having a structure with minute crackedpores which is obtained by sintering a composition in which a clayey rawmaterial that is contracted when heated and slags that are expanded whenheated are mixed has been known.

In addition, a porous ceramic sintered body having a structure withconsecutive through holes which is obtained by adding an alkali solutionto metallic aluminum so as to generate hydrogen in a water-containingcomposition and then sintering the composition has been known.

Recently, a porous ceramic sintered body is also used for a greeningbase material. The greening base material is laid under soil for growingground cover plants and needs to have an easy water infiltration and aproper water retentivity. This greening base material is laid on theroof of buildings or the like and plants are grown thereon. According tothis, the cooling effect of buildings may be improved.

A porous ceramic sintered body used for a greening base material isproposed in which diatomaceous earth is used as a raw material and amolding body of diatomaceous earth is sintered (for example, PTL 1).Since the porous ceramic sintered body has a binary structure in whichmicro air holes derived from diatomaceous earth are connected withmillimeter-sized tunnel structure voids formed artificially, the porousceramic sintered body has easy water infiltration and good waterretentivity.

CITATION LIST Patent Literature

-   [PTL 1] Japanese Unexamined Patent Application, First Publication    No. 2005-239467

SUMMARY OF INVENTION Technical Problem

However, in addition to easy water infiltration and proper waterretentivity, the porous ceramic sintered body used for a greening basematerial is desired to have good water diffusivity (diffusivity),particularly, to have diffusivity in a horizontal direction. Further,water, which is retained in air holes of the porous ceramic sinteredbody, has to be used in plants to be grown. Furthermore, in the porousceramic sintered body, the further improvement of the cooling effect isdesired.

To address the above-described circumstances, an object of the presentinvention is to provide a porous ceramic sintered body which is suitablefor plant growth and which has a high cooling effect.

Solution to Problem

A porous ceramic sintered body according to the present inventionincludes a pore volume, which is the total volume of pores with adiameter of 3 nm to 360 μm, of 0.2 cm³/g or larger and includes amicropore volume ratio of 30% by volume or more, in which the microporevolume ratio equals to the total volume of pores with a diameter equalto or greater than 0.01 μm and less than 1 μm divided by the porevolume.

It is preferable that a median pore diameter of pores with a diameter of3 nm to 360 μm be smaller than 40 μm. It is preferable that the porousceramic sintered body preferably include a layer-like dense layer havinga bulk specific gravity of 0.7 g/cm³ or more and a non-dense layerhaving a bulk specific gravity of less than 0.7 g/cm³. It is morepreferable that the non-dense layer be provided on both surfaces of thedense layer. The porous ceramic sintered body may be used as a greeningbase material.

Advantageous Effects of Invention

An object of the present invention is to provide a porous ceramicsintered body which is suitable for plant growth and which has a highcooling effect.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional photograph of a porous ceramic sintered bodyaccording to an embodiment of the present invention.

FIG. 2( a) is an electron microscopic photograph (magnification 30) ofthe cross section of a dense layer of the porous ceramic sintered bodyshown in FIG. 1. FIG. 2( b) is an electron microscopic photograph(magnification 2,000) in which a portion of the cross section of FIG. 2(a) is zoomed.

FIG. 3 is a cross-sectional photograph of a porous ceramic sintered bodyof Comparative Example.

FIG. 4 is a chart showing a measurement result of the pore volume of adense layer of a porous ceramic sintered body of Example.

FIG. 5 is a chart showing a measurement result of the pore volume of afirst non-dense layer of the porous ceramic sintered body of Example.

FIG. 6 is a chart showing a measurement result of the pore volume of theporous ceramic sintered body of Comparative Example.

FIG. 7 is a schematic diagram illustrating a test method of diffusivity(horizontal direction).

FIG. 8A is a schematic diagram illustrating a test method of diffusivity(15° inclination).

FIG. 8B is a schematic diagram illustrating a test method of diffusivity(15° inclination).

FIG. 9 is a graph showing a result of a plant growth test.

FIG. 10A is a graph showing a measurement result of an evaporation rate.

FIG. 10B is a graph showing a measurement result of an evaporation rate.

DESCRIPTION OF EMBODIMENTS

(Porous Ceramic Sintered Body)

Hereinafter, a plate-like porous ceramic sintered body (hereinafter,referred to as a plate-like ceramic body in some cases) according to anembodiment of the present invention will be described referring to thedrawing. FIG. 1 is a cross-sectional view of a plate-like ceramic body 1according to the embodiment of the present invention.

As shown in FIG. 1, the plate-like ceramic body 1 is schematicallyconfigured to include a dense layer 10, a first non-dense layer 20provided on one surface of the dense layer 10, and a second non-denselayer 30 provided on the other surface of the dense layer 10. That is,the plate-like ceramic body 1 has a three-layer structure consisting ofthe dense layer 10, the first non-dense layer 20, and the secondnon-dense layer 30.

An opening in which an air hole formed on the first non-dense layer 20is exposed is formed on a first surface 22 that is the surface of thefirst non-dense layer 20. An opening in which an air hole formed on thesecond non-dense layer 30 is exposed is formed on a second surface 32that is the surface of the second non-dense layer 30.

A thickness T1 of the plate-like ceramic body 1 may be determineddepending on uses. For example, the thickness T1 may be determined in arange of 0.5 to 15 cm and preferably in a range of 1.5 to 10 cm.

<Dense Layer>

The dense layer 10 is a layer in which pores with a diameter of 3 nm to360 μm (hereinafter, simply referred to as pores in some cases) areformed.

In the dense layer 10, as shown in FIG. 2( a), two or more voids 12,which are air holes with a diameter of larger than 360 μm, are formedand, as shown in FIG. 2( b), two or more pores 14 are formed.

The pores 14 or the voids 12 formed in the dense layer 10 formcommunication holes which communicate with each other. By forming thecommunication holes, the water retentivity, the diffusivity, and thecooling effect are improved.

The pore volume of the dense layer 10, that is, the total value of thevolume of all pores 14, is 0.2 cm³/g or larger, preferably 0.25 cm³/g orlarger, and more preferably 0.3 cm³/g or larger. When the pore volumethereof is smaller than the lower limit described above, the diffusivityin the plate-like ceramic body 1 is insufficient or the waterretentivity therein is insufficient. In addition, the upper limit of thepore volume may be determined depending on uses of the plate-likeceramic body 1 and, for example, the upper limit thereof is preferably0.8 cm³/g or smaller, more preferably 0.6 cm³/g or smaller, and stillmore preferably 0.4 cm³/g or smaller. When the pore volume exceeds theupper limit described above, water is difficult to evaporate and thusthe cooling effect may be deteriorated.

The pore volume is a value measured based on JIS R1655-2003.

The total value of volume of the pores 14 in the dense layer 10 per unitvolume (the volume of pores per unit volume) may be determined inconsideration of uses or the like of the plate-like ceramic body 1 and,for example, the total value thereof is preferably 0.1 to 0.5 cm³/cm³,and more preferably 0.2 to 0.4 cm³/cm³. When the total value thereof issmaller than the lower limit described above, the water retentivity andthe diffusivity may be insufficient. When the total value thereofexceeds the upper limit described above, the strength of the plate-likeceramic body 1 may be insufficient.

The ratio of the micropore volume to the pore volume (micropore ratio)which is the total value of volume of pores with a diameter of equal toor greater than 0.01 μm and smaller than 1 μm (hereinafter, referred toas micropores in some cases) in the pores 14, is 30% by volume or moreof the pore volume, more preferably 40% by volume or more, and stillmore preferably 50% by volume or more. When the ratio thereof is lessthan the lower limit described above, the water retentivity and thediffusivity are insufficient. The upper limit of the micropore ratio isnot particularly limited but may be 100% by volume. The micropore ratiois obtained by using the following formula (1).

Micropore ratio(% by volume)=micropore volume÷pore volume×100  (1)

The micropore volume of the dense layer 10 may be determined inconsideration of uses or the like of the plate-like ceramic body 1 aslong as the micropore ratio is 30% by volume or more. For example, whenthe plate-like ceramic body 1 is used for the greening base material,the micropore volume thereof is preferably 0.1 cm³/g or larger, morepreferably 0.12 cm³/g or larger, still more preferably 0.14 cm³/g orlarger, and particularly preferably 0.2 cm³/g or larger. When themicropore volume thereof is smaller than the lower limit describedabove, the diffusivity in the plate-like ceramic body 1 may beinsufficient or the water retentivity therein may be insufficient. Inaddition, the upper limit of the micropore volume in the dense layer 10may be determined in consideration of uses or the like of the plate-likeceramic body 1. For example, when the upper limit thereof is preferably0.8 cm³/g or less, more preferably 0.6 cm³/g or less, and still morepreferably 0.4 cm³/g or less. When the micropore volume exceeds theupper limit described above, water is difficult to evaporate and thusthe cooling effect may be deteriorated.

The micropore volume is a value measured by the same method as the porevolume.

When the volume of the voids 12 of the dense layer 10 is too small, athermal insulating property may be deteriorated. When the volume thereofis too large, the water retentivity may be deteriorated. Therefore, thevolume of the voids 12 may be determined in consideration of uses or thelike of the plate-like ceramic body 1.

The median pore diameters of pores with a diameter of 3 nm to 360 μm maybe smaller than 40 μm. The median pore diameters thereof may bepreferably 30 μm or smaller, more preferably 20 μm or smaller, and stillmore preferably 10 μm or smaller. In addition, the median pore diametersof pores with a diameter of 3 nm to 360 μm may be 10 nm or larger. Themedian pore diameters thereof may be preferably 100 nm or larger.

When the median pore diameter is smaller than 40 μm, the waterretentivity is excellent and thus it is possible to continuouslyevaporate water from the ceramic sintered body for a long time.

Moreover, when the median pore diameter is smaller than 10 nm, the waterretentivity is deteriorated and thus it may be difficult to continuouslyevaporate a sufficient amount of water from the ceramic sintered bodyfor a long time.

The bulk specific gravity of the dense layer 10 is 0.7 g/cm³ or more,preferably 0.75 to 0.95 g/cm³, and more preferably 0.8 to 0.9 g/cm³.When the bulk specific gravity thereof is less than the lower limitdescribed above, the strength of the plate-like ceramic body 1 may beinsufficient, the water retentivity may be deteriorated, or thediffusivity may be deteriorated. When the bulk specific gravity thereofexceeds the upper limit described above, water may be difficult toevaporate and thus the cooling effect may be deteriorated or water maybe difficult to infiltrate.

The porosity of the dense layer 10 may be determined in consideration ofuses or the like of the plate-like ceramic body 1. For example, theporosity thereof is preferably 40% by volume or more, is more preferably60 to 90% by volume, is even more preferably 65 to 80% by volume, and isstill more preferably 70 to 80% by volume. When the porosity thereof isless than the lower limit described above, the speed of the waterdiffusivity in the plate-like ceramic body 1 may be deteriorated. Whenthe porosity thereof exceeds the upper limit described above, the waterretentivity may be deteriorated or the strength of the plate-likeceramic body 1 may be deteriorated.

A thickness t1 of the dense layer 10 may be determined in considerationof uses, the thickness T1 of the plate-like ceramic body 1 or the like,and, for example, the thickness t1 thereof is determined preferably tobe in a range of 20 to 60% of the thickness T1.

<First Non-Dense Layer>

The first non-dense layer 20 is a layer in which pores are formed. Asshown in FIG. 1, in the first non-dense layer 20, two or more voids 24and two or more pores which are not shown in the drawing are formed, anda communication hole in which the void 24 and the pore communicate witheach other is formed.

The pore volume of the first non-dense layer 20 is 0.2 cm³/g or larger,preferably 0.3 to 0.6 cm³/g, and more preferably larger than 0.4 cm³/gand 0.5 cm³/g or smaller. When the pore volume thereof is smaller thanthe lower limit described above, the diffusivity in the plate-likeceramic body 1 is insufficient or the water retentivity therein isinsufficient. When the pore volume exceeds the upper limit describedabove, water is difficult to evaporate and thus the cooling effect maybe deteriorated.

The volume of pores per unit volume to the first non-dense layer 20 isthe same as the volume of pores per unit volume to the dense layer 10.

In the embodiment, the volume of pores per unit volume in the firstnon-dense layer 20 is considered to be smaller than the volume of poresper unit volume in the dense layer 10. By setting the volume of poresper unit volume in the first non-dense layer 20 to be smaller than thatof the dense layer 10, the water retentivity and the diffusivity areimproved while maintaining a sufficient strength of the plate-likeceramic body 1.

The micropore ratio of the first non-dense layer 20 is the same as themicropore ratio of the dense layer 10.

The micropore volume of the first non-dense layer 20 may be determinedin consideration of uses or the like and, for example, the microporevolume thereof is preferably 0.1 cm³/g or larger, more preferably 0.12to 0.8 cm³/g, and still more preferably 0.14 to 0.4 cm³/g. When themicropore volume thereof is smaller than the lower limit describedabove, the diffusivity may be deteriorated. When the micropore volumethereof exceeds the upper limit described above, water is difficult toevaporate and thus the cooling effect may be deteriorated.

When the volume of the voids 24 of the first non-dense layer 20 is toosmall, the thermal insulating property may be deteriorated or water isdifficult to infiltrate. In addition, when the volume of the voids 24 istoo large, the strength of the plate-like ceramic body 1 may bedeteriorated. Therefore, the volume of the voids 24 may be determined inconsideration of uses or the like of the plate-like ceramic body 1.

The median pore diameters of pores with a diameter of 3 nm to 360 μm maybe smaller than 40 μm. The median pore diameter thereof may preferablybe 30 μm or smaller, more preferably be 20 μm or smaller, and still morepreferably be 10 μm or smaller. In addition, the median pore diametersof pores with a diameter of 3 nm to 360 μm may be 10 nm or larger. Themedian pore diameters thereof may be preferably 100 nm or larger.

When the median pore diameters thereof are smaller than 40 μm, the waterretentivity is excellent and thus it is possible to continuouslyevaporate water from the ceramic sintered body for a long time.

Moreover, when the median pore diameters thereof are smaller than 10 nm,the water retentivity is deteriorated and thus it may be difficult tocontinuously evaporate a sufficient amount of water from the ceramicsintered body for a long time.

The bulk specific gravity of the first non-dense layer 20 is less than0.7 g/cm³, preferably 0.4 g/cm³ or more and less than 0.7 g/cm³, andmore preferably 0.5 to 0.65 g/cm³. When the bulk specific gravitythereof exceeds the upper limit described above, water permeability maybe deteriorated or water may be difficult to evaporate and thus it maybe difficult to obtain a good cooling effect. In addition, when the bulkspecific gravity thereof is less than the upper limit described above,the thermal insulating property or the sound insulating property of theplate-like ceramic body 1 is improved. When the bulk specific gravitythereof is less than the lower limit described above, the strength ofthe plate-like ceramic body 1 may be deteriorated or the evaporation ofwater is too fast and thus it may be difficult to maintain the coolingeffect.

The porosity of the first non-dense layer 20 may be determined inconsideration of uses or the like of the plate-like ceramic body 1. Forexample, the porosity thereof is preferably 50% by volume or more,preferably 60 to 90% by volume, and more preferably more than 80% byvolume and 90% by volume or less. When the porosity thereof is less thanthe lower limit described above, it may be difficult for water toinfiltrate therein. When the porosity thereof exceeds the upper limitdescribed above, the strength of the plate-like ceramic body 1 maydeteriorate.

In the embodiment, the porosity of the first non-dense layer 20 isconsidered to be larger than that of the porosity of the dense layer 10.When the porosity of the first non-dense layer 20 is considered to belarger than that of the porosity of the dense layer 10, the thermalinsulating property or the sound insulating property of the plate-likeceramic body 1 is further improved.

A thickness t2 of the first non-dense layer 20 may be determined inconsideration of uses, the thickness T1 of the plate-like ceramic body 1or the like, and, for example, the thickness t2 thereof is determined topreferably be in a range of 20 to 40% of the thickness T1.

<Second Non-Dense Layer>

The second non-dense layer 30 is a layer in which pores are formed. Asshown in FIG. 1, in the second non-dense layer 30, two or more voids 34and two or more pores which are not shown in the drawing are formed anda communication hole in which the void 34 and the pore communicate witheach other is formed.

The pore volume of the second non-dense layer 30 is the same as the porevolume of the first non-dense layer 20 and the volume of pores per unitvolume in the second non-dense layer 30 is the same as that of the firstnon-dense layer 20.

The micropore volume of the second non-dense layer 30 is the same as themicropore volume of the first non-dense layer 20 and the micropore ratioof the second non-dense layer 30 is the same as the micropore ratio ofthe first non-dense layer 20.

The median pore diameters of the pores with a diameter of 3 nm to 360 μmin the second non-dense layer 30 is the same as that of pores with adiameter of 3 nm to 360 μm in the first non-dense layer 20.

The bulk specific gravity of the second non-dense layer 30 is the sameas the bulk specific gravity of the first non-dense layer 20 and theporosity of the second non-dense layer 30 is the same as the porosity ofthe first non-dense layer 20.

The thickness t3 of the second non-dense layer 30 is the same as thethickness t2 of the first non-dense layer 20.

(Manufacturing Method)

A manufacturing method of the plate-like ceramic body 1 includes amixing step of mixing raw materials to obtain a mixture, a molding stepof molding the mixture to obtain a molding body, and a calcination stepof calcining the molding body.

<Mixing Step>

The mixing step is a step in which diatomaceous earth, clays, organicsludge, and slag are mixed to obtain a mixture. By blending as describedabove, a plate-like ceramic body having pores formed in the diatomaceousearth and pores, which are formed in such a manner that the weight ofthe organic sludge is decreased during sintering, is obtained.

<<Diatomaceous Earth>>

The diatomaceous earth used in the present invention is a depositconsisting of the remains of diatoms and is a porous material havingmicrometer-order air holes.

The diatomaceous earth is not particularly limited but the same materialas a material that is traditionally used for an insulating refractorybrick, a filtration material and the like may be used. For example, itis not necessary to fractionally purify an adulterated material of clayminerals (such as montmorillonite), quartz, feldspar and the like and,with recognition of the amount thereof, it is possible to adjust theblending quantity thereof to the mixture.

The moisture content of the diatomaceous earth is not particularlylimited but, for example, the moisture content of the diatomaceous earthin a natural drying state is preferably 20 to 60% by mass, morepreferably 30 to 50% by mass, and still more preferably 35 to 45% bymass. The reason is that, when the moisture content thereof is withinthe above-described range, by using the diatomaceous earth after coarseparticles in the adulterated material are removed during mixing inconsideration of the moisture content, it is possible to obtain amixture with a good moldability.

The moisture content is a value obtained in such a manner that a sampleis dried (200° C., for 12 minutes) using an infrared moisture gaugehaving a specification described below, and is calculated by thefollowing formula (2) in a loss on drying method.

<Specification>

Measuring method: loss on drying method (drying by heating and massmeasurement method)

Minimum readability: moisture content; 0.1% by mass

Measurement range: moisture content; 0.0 to 100% by mass

Drying temperature: 0 to 200° C.

Measurement accuracy: 5 g or more of sample mass and moisture content of±0.1% by mass

Thermal source: infrared lamp; 185 W

Moisture content(% by mass)=[(m ₁ −m ₂)/(m ₁ −m ₀)]×100  (2)

m₁: total mass (g) being summation of the mass of a container beforedrying and the mass of a sample before drying

-   -   m₂: total mass (g) of mass of the container after drying and        mass of the sample after drying    -   m₀: mass (g) of the container after drying

The blending quantity of the diatomaceous earth in the mixture may bedetermined in consideration of the pore volume, the micropore volume andthe like of the dense layer 10, the first non-dense layer 20 or thesecond non-dense layer 30. For example, the blending quantity thereof ispreferably 55% by mass or less, and is more preferably 1 to 45% by mass.When the blending quantity thereof is within the above-described range,it is possible to control the pore volume and the micropore ratio of thedense layer 10, the first non-dense layer 20 and the second non-denselayer 30 to be suitable without imparting the moldability of themixture.

<<Clays>>

Clays used in the present invention are a mineral material having clayeyproperties which are generally used as a raw material of the ceramicsindustry and are a material other than the diatomaceous earth.Well-known clays, which are used for a ceramic sintered body, may beused and it is preferable that clays be configured to have a mineralcomposition of quartz, feldspar, clayey materials or the like, havekaolinite as a main constituent mineral, and contain halloysite,montmorillonite, or illite. Among these, from the viewpoint ofsuppressing the crack progress during sintering and preventing thebreaking of the plate-like ceramic body 1, it is more preferable thatclays contain coarse particles of quartz with a particle diameter of 500μm or larger. The particle diameters of the coarse particles of quartzare preferably 5 mm or smaller. As the above-described clays, forexample, gairome clay or the like is exemplified. One kind of clays maybe used alone, or two or more kinds of clays may be used in combination.

The blending quantity of the clays in the mixture may be determined inconsideration of uses or moldability of the plate-like ceramic body 1.For example, the blending quantity thereof is preferably 5 to 60% bymass, is preferably 5 to 45% by mass, and is more preferably 10 to 40%by mass.

When the blending quantity thereof is within the above-described range,it is possible to smoothly perform molding without imparting themoldability of the mixture and to make the strength of the plate-likeceramic body 1 sufficient.

<<Organic Sludge>>

The organic sludge is sludge containing organic matter as a maincomponent. Arbitrary organic sludge may be used, and activated sludgederived from sewerage or an effluent treatment of factories or the likeis particularly preferable. The activated sludge is discharged fromeffluent treatment facilities using an activated sludge method throughaggregation and dehydration processes. By using the organic sludge asdescribed above, it is possible to form pores or micropores. Moreover,the activated sludge derived from an effluent treatment which isconsidered as waste materials may be recycled as a raw material.

The moisture content of the organic sludge is, for example, preferably60 to 90% by mass and is more preferably 65 to 85% by mass. The reasonis that, when the moisture content thereof is within the above-describedrange, it is possible to obtain a homogenous mixture in the mixing stepdescribed later and to maintain good moldability in the molding step.

The content of the organic matter in the organic sludge is notparticularly limited but, for example, the amount of organic matter(organic matter content) in the solid content of the organic sludge ispreferably 70% by mass or greater, and is more preferably 80% by mass orgreater. The upper limit of the organic matter content may be 100% bymass. The reason is that, as the organic matter content becomes greater,the pores are easily formed. The organic matter content is a valueobtained in such a manner that the ash content (% by mass) of the sludgeafter drying is measured at the carbonization temperature of 700° C.based on JIS M8812-1993 and is calculated by the following formula (3).

Organic matter content(% by mass)=100(% by mass)−ash content(% bymass).  (3)

The average particle diameter of the organic sludge may be determineddepending on the uses of the plate-like ceramic body 1. The averageparticle diameter thereof is preferably 1 to 5 μm and is more preferably1 to 3 μm. As the average particle diameter thereof becomes smaller, thepores in the dense layer 10 are easily formed. The average particlediameter is a median diameter on a volumetric basis (diameter of 50% byvolume) measured by a particle size distribution analyzer (LA-920,manufactured by Horiba Ltd.).

The amount of organic sludge to be used in the mixture may be determinedin consideration of uses or moldability of the plate-like ceramic body1. For example, the blending quantity thereof is preferably 1 to 50% bymass, is more preferably 5 to 30% by mass, and is still more preferably5 to 20% by mass. The reason is that, when the blending quantity thereofis within the above-described range, the mixture obtains a moderate flowproperty and plastic property such that the moldability is improved andit is possible to smoothly perform molding without blocking a moldingapparatus. Moreover, it is possible to make the pore volume and themicropore ratio of the dense layer 10, the first non-dense layer 20 orthe second non-dense layer 30 preferable.

<<Slag>>

The slag is not particularly limited but examples of the slag includeblast furnace slag generated when refining metal, urban waste moltenslag generated when melting urban waste, sewage sludge molten slaggenerated when melting sewage sludge, and glass slag such as castingiron slag generated when casting ductile cast iron or the like. Amongthese, the casting iron slag is more preferable in which a stablefoaming state is obtained because of the stable composition thereof andthe foaming rate thereof is 1.5 to 2 times compared to other slag. Byblending the slag, the voids 12, 24, and 34 are formed and thus thedegradation in the coefficient of water permeability (speed at whichwater is allowed to pass) may be suppressed.

The amount of slag to be used in the mixture may be determined inconsideration of uses or moldability of the plate-like ceramic body 1.For example, the blending quantity thereof is preferably 80% by mass orless, is more preferably 30 to 70% by mass, and is still more preferably40 to 60% by mass. When the blending quantity thereof is within theabove-described range, it is possible to smoothly perform moldingwithout imparting the moldability of the mixture and to set the porosityor the bulk specific gravity of the plate-like ceramic body 1 to be in apreferable range.

<<Arbitrary Component>>

In the mixture, arbitrary components may be blended within a range notimpairing the object of the present invention. Examples of the arbitrarycomponents include a naphthalene-based plasticizer such as Mighty 2000WH(trade name, manufactured by Kao Corporation); a melamine-basedplasticizer such as Melment F-10 (trade name, manufactured by ShowaDenko K. K.); a polycarboxylic acid-based plasticizer such as DarexSuper 100pH (trade name, manufactured by Grace Chemicals K.K.); anantimicrobial agent such as silver, copper, and zinc; an adsorptionagent such as zeolite and apatite; and metallic aluminum.

When the arbitrary components are blended into the mixture, it ispreferable that the amount of arbitrary components be determined in arange of 5 to 10% by mass, for example.

Moreover, when the organic sludge is blended at a preferable blendingratio in the mixing step, water may not be added in the mixing stepbecause water is contained in the organic sludge, or water may beappropriately blended in order to adjust the flow property or the likeof the mixture.

The moisture content of the mixture is not particularly limited but, forexample, the moisture content thereof is preferably 25 to 45% by massand more preferably 25 to 30% by mass. The reason is that, when themoisture content is within the above-described range, the mixture hasmoderate flow properties and plastic properties, and thus it is possibleto maintain a good moldability.

The mixing order of each component in the mixing step is notparticularly limited and, for example, a method in which thediatomaceous earth, the clays, the organic sludge, and the slag are putinto a mixing apparatus at once and mixed (one-step mixing method) is anexemplary example. In addition, for example, a mixture may be obtainedin such a manner that a primary mixture is obtained by mixing thediatomaceous earth and the organic sludge (first mixing operation) andthen the mixture is obtained by mixing the primary mixture, the clays,and the slag (second mixing operation) (hereinbefore, two-step mixingmethod). Since the organic sludge has a high flow property compared tothe clays, it is assumed that the organic sludge preferentially goesinto air holes of the diatomaceous earth during mixing. By molding andcalcining this mixture, it is considered that the organic matter of theorganic sludge with which the air holes of the diatomaceous earth arefilled is volatilized and the air holes of the diatomaceous earth aremaintained in proportion as the air holes of the diatomaceous earth arefilled with the organic sludge.

In the second mixing operation, the diatomaceous earth may be furtheradded.

It is preferable that the mixing step include the first mixing operationand the second mixing operation. First, in the first mixing operation,by mixing the diatomaceous earth and the organic sludge, a primarymixture with a moderate flow property is obtained and the air holes ofthe diatomaceous earth are filled with the organic sludge. Subsequently,in the second mixing operation, by mixing the primary mixture withmoderate flow properties, the clays, and slag, a homogenous mixture isstably obtained. Since the air holes of the diatomaceous earth arealready filled with the organic sludge in the second mixing operation,the clays do not easily go into the air holes of the diatomaceous earth.Therefore, the mixture obtained by the two-step mixing method has ahigher ratio of the air holes of the diatomaceous earth which are filledwith the organic sludge, compared to the mixture obtained by theone-step mixing method. As a result, by using the two-step mixing methodas the mixing step, it is considered that more air holes of thediatomaceous earth are maintained without being blocked.

The mixing apparatus used in the mixing step is not particularly limitedbut a well-known mixing apparatus may be used.

For example, examples of the mixing apparatus include a kneading machinesuch as Mix Muller (manufactured by Toshin Industry Co., Ltd.); akneader (manufactured by MORIYAMA COMPANY LTD.); and a mixing machine(manufactured by NITTO KAGAKU Co., Ltd.).

The mixing time in the mixing step may be determined in consideration ofthe blending ratio of the diatomaceous earth, the clays, the organicsludge and the slag, or the flow properties or the like of the mixture.It is preferable that the mixing time be determined such that themixture is in a plastic state. For example, the mixing time ispreferably in a range of 15 to 45 minutes and more preferably in a rangeof 25 to 35 minutes.

The temperature in the mixing step is not particularly limited but thetemperature may be determined in consideration of the blending ratio ofthe diatomaceous earth, the clays, the organic sludge and the slag; themoisture content; or the like. For example, the temperature ispreferably in a range of 40 to 80° C. and is more preferably in a rangeof 50 to 60° C.

<Molding Step>

The molding step is a step in which the mixture obtained in the mixingstep is molded in an arbitrary shape.

A well-known molding method may be used for a molding method and themolding method may be determined in consideration of characteristics ofthe mixture or a shape of the porous ceramic sintered body. Examples ofthe molding method include a method of obtaining an arbitrary plate-likemolding body using a molding machine; a method of obtaining a moldingbody by filling a mixture into an arbitrary shape mold; or a method inwhich a mixture is stretched or rolled and then the mixture is cut intoan arbitrary size.

Examples of the molding machine include a vacuum earth kneading andmolding machine; a flat plate press molding machine; and a flat plateextruding and molding machine. Among these, vacuum earth kneading andmolding machine is preferable. By removing air in a molding body usingvacuum earth kneading and molding machine, it is possible to control themicropore ratio of the dense layer 10.

<Calcination Step>

The calcination step is a step in which the molding body obtained in themolding step is dried (drying operation), the dried molding body iscalcined (calcination operation), and the diatomaceous earth, the claysand the like are sintered, thereby obtaining a porous ceramic sinteredbody.

<<Drying Operation>>

The drying operation is not particularly limited but a well-known methodmay be used. For example, a molding body may be naturally dried or maybe dried under heat at 50 to 220° C. in a hot air drying furnace for anarbitrary time. The moisture content of the dried molding body is notparticularly limited but, for example, the moisture content thereof ispreferably less than 5% by mass and is more preferably less than 1% bymass. The moisture content of the dried molding body may be 0% by massas a lower limit.

<<Calcination Operation>>

A calcination method is not particularly limited but a well-known methodmay be used. For example, a method in which calcination is performed atan arbitrary temperature using a continuous sintering furnace such as aroller hearth kiln or a batch-wise sintering furnace such as a shuttlekiln is an exemplary example of a calcination method. Among these, fromthe viewpoint of productivity, a continuous sintering furnace ispreferably used in calcining

The calcination temperature (reaching temperature) may satisfy acondition in which the diatomaceous earth and the clays are sintered,organic matter contained in the organic sludge is volatized by thermaldecomposition so as to lose weight thereof, and the slag is expanded.The calcination temperature may be determined in consideration of theblending ratio of the diatomaceous earth, the clays, the organic sludgeand the slag, or in consideration of the components or the like of theorganic sludge. For example, the calcination temperature is preferably950 to 1,200° C. and is more preferably 1,000 to 1,100° C. Most of theorganic matter is started to be decomposed at around 700° C., a uniquesmell of the organic sludge is thermally decomposed at 950° C. so as tosolve the smell problem, and most of the organic matter in the organicsludge is volatilized so as to reduce the weight thereof. Moreover, mostof the slag is expanded by crystallization at 800 to 850° C.

When the calcination temperature exceeds 1,200° C., the entirecompositions of the porous ceramic sintered body are vitrified and thusthe molding body may be broken or pores or voids may be blocked.

In the calcination step, until the temperature reaches the calcinationtemperature, moisture is firstly evaporated from the molding body andthereafter organic matter of the activated sludge is volatilized throughthermal decomposition. In this process, by appropriately adjusting thetemperature increase (heat curve and temperature gradient), it ispossible to suppress a drastic evaporation of moisture or a drasticvolatilization of organic matter, and thus pulverization (blasting) ofthe molding body may be prevented. In addition, there is a case wheredamage such as breaking or pulverization occurs in the porous ceramicsintered body due to a drastic cooling after a temperature is reached atthe calcination temperature. This phenomenon is most prevalent whenusing a continuous sintering furnace. Therefore, in the calcinationstep, it is preferable that a temperature gradient be provided.

The temperature gradient may be determined in consideration of the sizeor the like of a calcination apparatus. For example, when calcination isperformed using a continuous sintering furnace having a calciningportion with an effective length of 15 m, it is preferable that thetemperature of an inlet port and of an outlet port of the continuoussintering furnace be set to a normal temperature (20° C.±15° C.), thatthe calcination temperature of a central portion of the continuoussintering furnace be set at 950° C. to 1,200° C., that the transit speedof the molding body in the continuous sintering furnace be set at 3 to 4mm/sec., and the temperature gradient condition be set as follows.

The continuous sintering furnace is divided into 10 zones with an equaldistance and the temperature gradient of the continuous sinteringfurnace is preferably 0.4 to 0.6° C./sec., 0.1 to 0.2° C./sec., 0.3 to0.4° C./sec., 0.4 to 0.6° C./sec., 0.7 to 1.0° C./sec., 0.004 to 0.005°C./sec., −0.4 to −0.2° C./sec., −0.8 to −0.5° C./sec., −0.4 to −0.3°C./sec., and −0.3 to −0.1° C./sec., from the inlet port side.

If the moisture content of the molding body exceeds 3% by mass when themolding body is put into the continuous sintering furnace, the moisturecontent in the calcination step is drastically evaporated and thusbursting or blasting may occur in the molding body or the activatedsludge is drastically volatilized and thus a damage may occur.Therefore, for example, by controlling the temperature gradient in thecontinuous sintering furnace as described above, it is possible tosuppress damage of the molding body in the calcination step. Moreover,by providing an appropriate temperature gradient, a three-layerstructure is formed or a communication hole is formed and thus it ispossible to enhance the water retentivity, the diffusivity, the waterpermeability or the cooling effect of the plate-like ceramic body 1.

The calcination time may be determined in consideration of thecalcination temperature, the moisture content of the mixture or thelike. For example, a residence time at the calcination temperature ispreferably in a range of 4 to 10 minutes and more preferable in a rangeof 6.5 to 7.5 minutes. When the residence time is within theabove-described range, it is possible to preferably perform calcinationwhile preventing damage of the plate-like ceramic body 1.

The plate-like ceramic body 1 obtained as described above may be usedwithout change or about 5 cm from the side end of the plate-like ceramicbody 1 may be cut off along four side surfaces so as to be used for agreening base material or the like. When the plate-like ceramic bodies 1are arranged next to each other and then used, it is preferable that 5cm from the side end of the plate-like ceramic body 1 be cut off alongthe four side surfaces, from the viewpoint of a good contact state ofthe side surfaces to each other.

The front surface of the plate-like ceramic body 1 may be ground using agrinder or the like. By grinding the front surface of the plate-likeceramic body 1, the speed of water absorption is improved. Moreover,when the plate-like ceramic body 1 is used for a greening base materialor the like, by grinding the front surface of the plate-like ceramicbody 1, a root of a plant is easy to get into the plate-like ceramicbody 1. Therefore, the firing of plants is prevented and the growth ofplants is promoted.

Since the pore volume is 0.2 cm³/g or larger and the micropore ratio is30% by volume or more, the plate-like ceramic body according to theembodiment has high water retentivity and diffusivity. The reason isthat water is immediately absorbed and retained by the capillary actionof communication holes. In addition, water infiltrating into theplate-like ceramic body is gradually evaporated and thus it is possibleto maintain the cooling effect for a long time.

As described above, since the plate-like ceramic body according to theembodiment has excellent water retentivity and diffusivity, theplate-like ceramic body according to the embodiment is suitable forplant growth and since the retained water is evaporated over a longperiod of time, the plate-like ceramic body according to the embodimenthas a high cooling effect.

Since the plate-like ceramic body according to the embodiment has athree-layer structure which is configured to include a dense layer witha bulk density of 0.7 g/cm³ or more and non-dense layers with a bulkspecific gravity of less than 0.7 g/cm³ that are formed on both surfacesof the dense layer, the plate-like ceramic body according to theembodiment has excellent thermal insulating property and soundinsulating property, and the water retentivity and the diffusivitythereof are improved while maintaining the water permeability. Forexample, when the first surface 22 is set to be the upper side in avertical direction and then water is poured to the first surface 22, thepoured water rapidly flows downward to reach to the dense layer 10,since the first non-dense layer 20 with a low bulk specific gravity hashigh water permeability. The water reaching to the dense layer 10 isdiffused to a horizontal direction as well as the lower side in thevertical direction, by the capillary action of communication holesformed in the dense layer 10. In this way, the water poured to the firstsurface 22 is rapidly diffused into the plate-like ceramic body 1 and isretained in the plate-like ceramic body 1.

Since the plate-like ceramic body according to the embodiment hasexcellent water retentivity and diffusivity and it is possible tomaintain a good cooling effect thereof for a long time, the plate-likeceramic body according to the embodiment is preferably used for agreening base material, plant cultivation equipment and a thermalinsulating material both indoors and outdoors. In addition, since theplate-like ceramic body according to the embodiment can suppresstemperature increases with respect to buildings or the surface of groundin which it is used, the plate-like ceramic body according to theembodiment is preferably used for a roofing material, an external wallmaterial or an embedded material which is embedded in the surface of theground or in the ground of a walking path or a parking area.Particularly, the plate-like ceramic body according to the embodiment ispreferably used as a greening base material.

According to the manufacturing method of the embodiment, since theplate-like ceramic body is obtained by molding and calcining the moldingbody in a state where the air holes of the diatomaceous earth are filledwith the organic sludge, organic matter of the organic sludge isvolatilized during sintering and it is possible to maintain the airholes of the diatomaceous earth. In addition, pores, which are formed byvolatilizing the organic matter of the organic sludge in the moldingbody during calcining, are formed in the plate-like ceramic body.Moreover, voids are formed in the plate-like ceramic body by expandingthe slug in the molding body during calcination. As a result, it ispossible to obtain a plate-like ceramic body having pores and voids.

Since the organic sludge has a high flow property compared to the clays,it is assumed that the organic sludge preferentially goes into air holesof the diatomaceous earth in the mixing step. It is considered that theorganic matter of the organic sludge in the air holes of thediatomaceous earth filled with the organic sludge is volatilized duringsintering and the air holes of the diatomaceous earth are maintained. Inaddition, by calcining the molding body containing the organic sludge,more pores are formed in the plate-like ceramic body by volatilizing theorganic matter of the organic sludge and a communication hole is formed.Moreover, since the mixing step includes the first mixing operation andthe second mixing operation, the entry of the clays into the air holesof the diatomaceous earth is effectively prevented and pores are easilyformed.

According to the manufacturing method of the present invention, it ispossible to obtain the plate-like ceramic body having a three-layerstructure. The reason why the three-layer structure is formed is assumedto be as follows. In the calcination step, first, the temperature in thevicinity of the front surface of the molding body becomes an arbitrarytemperature, pores and voids are formed, and the first and secondnon-dense layers are provided through calcination. Next, the temperaturein the vicinity of the central portion of the molding body becomes anarbitrary temperature and pores and voids are formed in the vicinity ofthe central portion. In this time, since air holes are formed in thevicinity of the front surface and sintering is already carried out, theslag in the vicinity of the central portion is not sufficiently expandedand thus the volume of the voids is difficult to increase. Therefore, itis considered that the dense layer having a higher bulk specific gravitythan that of the non-dense layers is formed between the first non-denselayer and the second non-dense layer.

According to the manufacturing method of the present invention, sincethe organic sludge which is considered to be a waste material from thepast is utilized as a raw material, the manufacturing method of thepresent invention is capable of responding preferably to environmentalaspects. In addition, the organic sludge is a raw material which can beeasily and massively obtained and has a raw material procurementadvantage. Moreover, since the moisture content of the organic sludge ishigh, the operation of adding water in the mixing step can be omitted.

The present invention is not limited to the above-described embodiment.

In the above-described embodiment, the porous ceramic sintered body isconsidered to be in a plate-like shape, but, in the present invention,it is preferable that the pore volume thereof be 0.2 cm³/g or larger andthe micropore ratio thereof be 30% by volume or more and the shape ofthe porous ceramic sintered body may be selected depending on the usagethereof. For example, the shape of the porous ceramic sintered body maybe a flowerpot shape, a pellet shape, or a granular shape in which theplate-like ceramic body is pulverized to about 1 to 50 mm squares.Moreover, in advance, the porous ceramic sintered body may be sinteredto be a granular shape with about 1 to 50 squares. The granular-shapedporous ceramic sintered body can be used without change or can be usedas a raw material of blocks or tiles which is used for a wall materialor a road surface material, and thus, by using the granular-shapedporous ceramic sintered body as described above, a material for buildingconstruction or a civil engineering material with excellent waterretentivity, diffusivity, water cooling, thermal insulation and soundinsulating property can be obtained.

In the above-described embodiment, the first and second non-dense layersare provided but the present invention is not limited thereto. Theporous ceramic sintered body may be configured to include only a denselayer, or to include only non-dense layers or the non-dense layer may beprovided on only one surface of the dense layer. The porous ceramicsintered body configured to include only a dense layer may be obtainedby adjusting the blending ratio and the calcination condition of eachraw material.

In the above-described embodiment, the dense layer and the non-denselayers are laminated but the present invention is not limited thereto.For example, the non-dense layer may be formed in such a manner that thenon-dense layer covers the dense layer as a core.

In the above-described embodiment, the voids are formed in the denselayer but the present invention is not limited thereto. The voids maynot be formed in the dense layer.

Moreover, in the above-described embodiment, the voids are formed in thenon-dense layer but the present invention is not limited thereto. Thevoids may not be formed in the non-dense layer.

The dense layer or the non-dense layer in which the voids are not formedmay be obtained by not blending slag into the molding body.

In the above-described embodiment, the diatomaceous earth is blendedinto the mixture but the present invention is not limited thereto. Thediatomaceous earth may not be blended into the mixture. By not blendingthe diatomaceous earth, it is possible to reduce the pore volume derivedfrom the diatomaceous earth.

EXAMPLE

Hereinafter, the present invention will be described in detail referringto Examples but the present invention is not limited to the followingdescription.

(Raw Material to be Used)

Raw materials used in Examples were as follows.

<Organic Sludge>

Activated sludge, which is discharged from effluent treatment facilitiesof a dyehouse (KOMATSU SEIREN Co., Ltd., Mikawa Factory) by an activatedsludge method through aggregation and dehydration processes, was used asthe organic sludge in the Examples described below. The organic mattercontent (with respect to the solid content) of the activated sludge was83% by mass.

<Clays>

Gairome clay (from Gifu-ken or Aichi-ken) was used as the clays.

<Diatomaceous Earth>

Powdered diatomaceous earth with a moisture content of 5% by mass thatis a raw material of an insulating firebrick from Noto Distriction wasused as the diatomaceous earth.

<Slag>

Casting iron slag was used as slag. This casting iron slag is ductilecasting iron slug in which the main components are SiO₂, Al₂O₃, CaO,Fe₂O₃, FeO, MgO, MnO, K₂O, and Na₂O.

Example 1

According to the composition of the mixture shown in Table 1, organicsludge and diatomaceous earth were mixed using Mix Muller (manufacturedby Toshin Industry Co., Ltd.), thereby obtaining a primary mixture(first mixing operation). Then, clays and slag were added to the primarymixture, followed by further mixing and thus a mixture in a plasticstate was obtained (second mixing operation). The obtained mixture wasmolded using a vacuum earth kneading and molding machine (manufacturedby Takahama Industry Co., Ltd.) and thus a strip-shaped primary moldingbody with a width of 60 cm and a thickness of 2 cm was obtained. Theprimary molding body was cut into an arbitrary pitch and width, therebyobtaining a substantially square plate-like molding body with athickness of 2 cm (molding step).

The obtained molding body was dried using a hot air drying machine (180°C., 0.5 hours) and the moisture content thereof was set to be 1% by massor less. Thereafter, using a continuous sintering furnace, the moldingbody was calcined under the calcination condition shown in Table 1.After the calcination, the side ends of the plate-like ceramic body werecut off along four side surfaces thereof, thereby obtaining a plate-likeceramic body having a width of 50 cm, a length of 50 cm, and a thicknessof 4 cm (A size), a plate-like ceramic body having a width of 25 cm, alength of 25 cm, and a thickness of 4 cm (B size), and a plate-likeceramic body having a width of 16.7 cm, a length of 16.7 cm, and athickness of 4 cm (C size) (calcination step). The both squareplate-like surfaces of the obtained plate-like ceramic bodies have nostructural difference and any surfaces can be used as a front surface ora back surface. The surface of the obtained plate-like ceramic body tobe ground using a grinder was set to be a front surface and the surfacethereof not to be ground was set to be a back surface. With respect toonly the front surface of the obtained plate-like ceramic body,approximately 1 mm of the surface was ground away using a grinder andthe back surface thereof was used without grinding.

For the dense layer and the first non-dense layer of the obtainedplate-like ceramic body, the pore volume, the volume of pores per unitvolume, the micropore volume, the micropore ratio, the bulk specificgravity and the porosity of the respective layers were obtained and thebending strength, the saturated moisture content, the moisture contentof a sample pole having each pF value, and the thermal conductivity ofthe plate-like ceramic body were measured.

Moreover, the cross section of the obtained plate-like ceramic body wasthe same as shown in FIG. 1.

As a continuous sintering furnace, a roller hearth kiln (effectivelength of sintering furnace: total length of 15 m, dividing thesintering furnace into zones 1 to 10 with a length of respectively 1.5m) was used.

Comparative Example 1

According to the composition of the mixture shown in Table 1,diatomaceous earth, clays, and slag were mixed using Mix Muller, therebyobtaining a mixture (mixing step). A molding body was obtained from theobtained mixture in a similar way to Example 1 and the molding body wascalcined, thereby obtaining plate-like ceramic bodies of A to C sizes.In a similar way to Example 1, with respect to only the front surfacesof the obtained plate-like ceramic bodies, 1 mm of the surfaces wereapproximately ground away using a grinder and the back surfaces thereofwere used without grinding.

For the obtained plate-like ceramic bodies, the pore volume, the volumeof pores per unit volume, the micropore volume, the micropore ratio, thebulk specific gravity, and the porosity thereof were obtained in asimilar way to Example 1 and the results are shown in Table 1. Moreover,the cross-sectional photograph of the obtained plate-like ceramic bodyis shown in FIG. 3.

(Measurement Method)<

<Bulk Specific Gravity>

External dimensions of a test piece of each layer were measured using acaliper and thus the volume thereof was obtained. The same test piecewas in an absolute dry state. Then, the mass thereof was measured usingan electric balance (absolute dry state mass) and the specific gravitythereof was calculated by the following formula (4). The number (N) ofsamples in each Example was set to be N=10.

Specific gravity(g/cm³)=[absolute dry state mass(g)]/[volume(cm³)]  (4)

<Porosity>

The porosity was measured based on JIS R2614-1985 by the followingformula (5). A true specific gravity is a specific gravity which ismeasured in a state where the test piece is pulverized so as to removeair holes.

Porosity(% by volume)=(true specific gravity−bulk specific gravity)÷truespecific gravity×100  (5)

<Pore Volume, Micropore Volume, Micropore Ratio, and Median PoreDiameter>

The plate-like ceramic body (A size) of each Example was cut in athickness direction and the respective layers of the dense layer, thefirst non-dense layer, and the second non-dense layer were cut into asize with a width of 15 mm, a length of 40 mm, and a thickness of 7 mm,thereby preparing test pieces. For the test pieces, the volume and themedian pore diameter of pores were measured based on JIS R1655 under thefollowing measurement conditions. The pore volume, the micropore volume,and the micropore ratio were calculated from the chart of themeasurement result.

<<Measurement Condition>>

Apparatus to be used: AutoPore 9420 (manufactured by MicromeriticsInstrument Corporation)

Mercury to be used: recycled mercury

Surface tension of mercury: 485 dynes/cm (0.485 N/m)

Contact angle of mercury: 130°

Measurement pressure: 0.5 to 60,000 psia (0.003 to 414 MPa)

A method of calculating will be described using FIG. 4. FIG. 4 is achart showing a measurement result of the pore volume of a dense layerof Example 1. The horizontal axis represents the diameter of pores, theright side of vertical axis represents volume of pores (unit porevolume) with a diameter in the horizontal axis, and the left side of thevertical axis represents a total volume of pores (total pore volume). Asshown in FIG. 4, the total volume of pores with a diameter of 3 nm to360 μm, that is, the pore volume was 0.29 cm³/g. The total volume ofpores with a diameter of 1 to 360 μm was 0.14 cm³/g and the total volumeof pores with a diameter of 0.01 to 360 μm was 0.28 cm³/g.

The above-described results were substituted into the following formula(6) and thus the micropore volume was obtained. The micropore ratio wasobtained from the obtained micropore volume and the pore volume.

The measurement result of the first non-dense layer is shown in FIG. 5and the measurement result of Comparative Example 1 is shown in FIG. 6.

Micropore volume=[total volume of pores with a diameter of 0.01 to 360μm]−[total volume of pores with a diameter of 1 to 360 μm]  (6)

<Volume of Pores per Unit Volume >

The volume of pores per unit volume was obtained by the followingformula (7).

Volume of pores per unit volume(cm³/cm³)=pore volume÷(1÷bulk specificgravity)  (7)

<Bending Strength>

The bending strength was measured based on JIS RS201.

<Saturated Moisture Content>

Samples (N=10) in which the specific gravities were measured wereimmersed in water for 60 minutes. Thereafter, with the front surfacesthereof facing up, the samples were taken out of water without beingtilted and the mass thereof (saturated state mass) was measured, therebyobtaining the saturated moisture content using the following formula(8). By taking the samples out of water without tilting them and withthe front surfaces thereof facing up, it is possible to prevent waterfrom flowing out of the samples.

Saturated moisture content(% by mass)=[(saturated state mass−absolutedry state mass)/absolute dry state mass×100  (8)

<Measurement of Moisture Content of Sample Pole Having Each pF Value>

For the plate-like ceramic body (A size) in each Example, the centralportion and portions in the vicinity of the four corners were cut out asubstantially cylindrical shape having a diameter of 42 mm, and athickness of 40 mm, and the cut portions in a saturatedmoisture-containing state were used as sample poles (five poles). Then,the sample poles were mounted on a dedicated rotor jig. The rotor jig onwhich the sample poles were mounted was mounted on a rotor (15B-R8 forpF measurement for soil) mounted on a centrifugal separator (Model:50B-5, manufactured by SAKUMA CO., LTD.) and the centrifugal treatmentwas carried out at 650 rpm for 30 minutes. At this time, the quantity ofwater separated from the sample poles was considered to be the moisturecontent of the sample pole having pF value of 1.5 or less.

Next, the sample poles were subjected to the centrifugal treatment at1,540 rpm for 30 minutes. Then, the quantity of water separated from thesample poles was considered to be the moisture content of the samplepole having pF value of more than 1.5 and 2.7 or less and the quantityof water remaining in the sample poles was considered to be the moisturecontent of the sample pole having pF value of more than 2.7.

The average mass of the five sample poles during drying was 46.4 g, theaverage mass of the five sample poles (saturated moisture-containingstate) was 73.8 g, the average value of moisture content of the samplepole having pF value of 1.5 or less in the five sample poles was 16.5 g,the average moisture content of the sample pole having pF value of morethan 1.5 and 2.7 or less in the five sample poles was 3.4 g, and theaverage moisture content of the sample pole having pF value of more than2.7 in the five sample poles was 7.5 g.

<Measurement of Thermal Conductivity>

A specimen was sliced in a length direction, a width direction, and athickness direction based on JIS A1412-2-1999 to have a length of 20 cm,a width of 20 cm, and a thickness of 21.6 mm and then a measurement wasperformed. The results were a heat current density of 45.7 W/m², atemperature of a high temperature side of 26.1° C., a temperature of alow temperature side of 16.8° C., an average temperature of the specimenof 21.5° C., a thermal resistance of 17.5 (m²·K)/W and a thermalconductivity of 0.123 W/(m·K).

TABLE 1 Comparative Example 1 Example 1 Mixture Organic Sludge (part bymass) 10 — Composition Diatomaceous Earth (part by mass) 5 5 Clays (partby mass) 30 35 Slag (part by mass) 55 60 Calcination CalcinationTemperature [Reaching 1050 1050 Condition Temperature] (° C.)Calcination Time (min) 65 65 Temperature Zone 1 (° C./sec.) 0.57 0.57Gradient Zone 2 (° C./sec.) 0.16 0.16 Zone 3 (° C./sec.) 0.33 0.33 Zone4 (° C./sec.) 0.52 0.52 Zone 5 (° C./sec.) 0.86 0.86 Zone 6 (° C./sec.)0.005 0.005 Zone 7 (° C./sec.) −0.34 −0.34 Zone 8 (° C./sec.) −0.72−0.72 Zone 9 (° C./sec.) −0.35 −0.35 Zone 10 (° C./sec.) −0.26 −0.26Structure Dense Layer Pore Volume (cm³/g) 0.29 0.43 Volume of Pores per0.26 0.21 Unit Volume (cm³/cm³) Micropore Volume 0.14 0.11 (cm³/g)Micropore Ratio (% by 48 26 volume) Bulk Specific Gravity 0.89 0.48(g/cm³) Porosity (% by volume) 67.8 82.5 Median Pore Diameter 1.00 40.1(μm) First Non-dense Pore Volume (cm³/g) 0.33 — Layer Volume of Poresper 0.20 — Unit Volume (cm³/cm³) Micropore Volume 0.15 — (cm³/g)Micropore Ratio (% by 47 — volume) Bulk Specific Gravity (g/cm³) 0.62 —Porosity (% by volume) 77.5 — Median Pore Diameter 1.10 — (μm) ResultBending Strength (N/mm²) 3.3 — Saturated Moisture Content (% by mass) 59— Moisture Content 1.5 or less (% by mass) 60.2 — of Sample Pole greaterthan 1.5 and 2.7 12.4 — having each pF or less (% by mass) Value greaterthan 2.7 (% by 27.4 — mass) Thermal Conductivity (W/(m · K)) 0.123 —

As shown in Table 1 and FIG. 1, the plate-like ceramic body of Example 1has a three-layer structure configured to include the dense layer, andthe non-dense layers provided on both sides of the dense layer. The porevolume thereof was 0.2 cm³/g or larger and the micropore ratio thereofwas 30% by volume or more.

On the other hand, as shown in FIG. 3, the plate-like ceramic body ofComparative Example 1 has a single-layer structure and voids,particularly, massive voids having a size measured by millimeters, wereshown in the entire cross section of the plate-like ceramic bodythereof. Moreover, the micropore ratio of the plate-like ceramic body ofComparative Example 1 was 26% by volume.

As shown in Table 1, Example 1 to which the present invention is appliedhad a bending strength of 3.3 N/mm² or greater and thus the bendingstrength thereof was a sufficient strength for use as a greening basematerial. Moreover, the moisture content of a sample pole having pFvalue of 2.7 or less was 72.6% by mass. Generally, water of a samplepole having a pF value of 2.7 or less may be used for the plant growth.According to this, it was found that water retained in the plate-likeceramic body of Example 1 was retained in a state where the plate-likeceramic body can be used as a greening base material.

Experimental Example 1 Diffusivity (in Horizontal Direction)

As shown in FIG. 7, four pieces of plate-like ceramic bodies (B size)100 of Example 1 were arranged to be a test bed 101. 4,000 cm³ of waterwas poured by a tube 120 to a position P in the vicinity of a topportion 102 of the test bed 101 (supply rate: 50 cm³/min., for 80minutes). The water was poured to the front surface of the plate-likeceramic body.

During the start of pouring water to the end of pouring water, waterleakage from the test bed 101 was not found. Moreover, the water to bepoured infiltrated the entire test bed 101.

From the above-described result, it was found that the plate-likeceramic body to which the present invention is applied has an excellentdiffusivity in a horizontal direction.

Experimental Example 2 Diffusivity (15° Inclination)

As shown in FIG. 8A, nine pieces of plate-like ceramic bodies (C size)110 of Example 1 were arranged to be a test bed 112. As shown in FIG.8B, the test bed 112 was disposed at an inclination angle θ=15° to ahorizontal surface such that the test bed 112 was directed from a firstside 114 downward a second side 116 facing the first side 114. 4,000 cm³of water was poured by the tube 120 to a position Q in the vicinity ofthe first side 114 (supply rate: 50 cm³/min., for 80 minutes). The waterwas poured to the front surface of the plate-like ceramic body. Duringthe start of pouring water to the end of pouring water, water leakagefrom the test bed 112 was not found. Moreover, the water to be pouredinfiltrated the entire test bed 112.

From the above-described result, it was found that the plate-likeceramic body to which the present invention is applied has excellentdiffusivity in a horizontal direction even in a case where theplate-like ceramic body was inclined by 15°.

Experimental Example 3 Plant Growth Test

The plate-like ceramic body (A size, dry mass: 6.9 kg) of Example 1 wasset to be in a saturated moisture-containing state. Then, artificialsoil for greening was laid on the front surface of the plate-likeceramic body to have a thickness of 1 cm and sedums were planted so asto make a greening base (kg). The two greening bases (greening bases Aand B) were prepared so as to be stored without irrigation with waterand then the growth situation of the sedum was observed and the massesof the greening bases were measured at 10 a.m. every day. The result ofthe mass measurement is shown in FIG. 9.

The artificial soil for greening used in this experiment was a mixtureof coconut shell mature compost: 50% by mass, vermiculite: 20% by mass,Kanuma earth (fine grain): 20% by mass, peat moss: 10% by mass, UnimixPlus II: 750 g/m³ and MAGAMP III BB-SS: 1 kg/m³.

FIG. 9 is a graph in which storage days is represented in a horizontalaxis and the mass of the greening base is represented in a verticalaxis. In the graph, an explanatory note (a) indicates the greening baseA and an explanatory note (b) indicates the greening base B. As shown inFIG. 9, the mass of the greening base A was 9.2 kg and the mass of thegreening base B was 10.1 kg at the first day of storage beginning. Afterstored without irrigation with water for 28 days, the mass of thegreening base A was 7.35 kg and the mass of the greening base B was 7.75kg. Moreover, the planted sedums were not fired even after a lapse of 28days. From the above-described results, it was assumed that a slightamount of moisture remained in the plate-like ceramic body in a case ofthe storage without irrigation with water for 28 days.

Experimental Example 4 Measurement of Evaporation Rate

Hereinafter, in Experimental Examples 4-1 and 4-2, the front surface andthe back surface of the plate-like ceramic body obtained in Example 1were used without grinding.

Experimental Example 4-1

The front surface of the plate-like ceramic body (A size, dry mass: 9.6kg) was irrigated with 2.64 kg of water and then was set to be a sample.This sample was disposed outside and then the mass transition of thesample was measured over 2 days. The irrigation was carried out at 5a.m. and the mass of the sample was measured every 1 hour to obtain anamount of reduction in the mass of the sample every 1 hour. FIG. 10Ashows the transition of amount of reduction in the mass of the sample atthe first day. In addition, after the sample was irrigated with 2.64 kgof water at 5 a.m. of the second day, the mass of the sample wasmeasured every 1 hour to obtain an amount of reduction in the mass ofthe sample every 1 hour. FIG. 10B shows the transition of amount ofreduction in the mass of the sample at the second day.

Experimental Example 4-2

An amount of reduction in the mass of the sample was obtained in asimilar way to Experimental Example 4-1, except that the plate-likeceramic body was changed to a plate-like ceramic single body andartificial soil for greening was laid on the front surface of theplate-like ceramic body (A size) to have a thickness of 1 cm and sedumswere planted, thereby preparing a sample. The results are shown in FIGS.10A and 10B.

Experimental Example 4-3

An amount of reduction in the mass of the sample was obtained in asimilar way to Experimental Example 4-1, except that, without using theplate-like ceramic body, artificial soil for greening was laid to have athickness of 80 mm. The results are shown in FIGS. 10A and 10B.

Experimental Example 4-4

An amount of reduction in the mass of the sample was obtained in asimilar way to Experimental Example 4-1, except that, without using theplate-like ceramic body, artificial soil for greening was laid to have athickness of 80 mm and Korean lawn grass was planted thereon. Theresults are shown in FIGS. 10A and 10B.

FIG. 10A is a graph showing the transition of amount of reduction in themass of the sample at the first day. The measurement time is representedin a horizontal axis and the amount of reduction in the mass of thesample is represented in a vertical axis. FIG. 10B is a graph showingthe transition of amount of reduction in the mass of the sample at thesecond day. The measurement time is represented in a horizontal axis andthe amount of reduction in the mass of the sample is represented in avertical axis. In FIGS. 10A and 10B, an explanatory note (c-1)represents the result of Experimental Example 4-1, an explanatory note(c-2) represents the result of Experimental Example 4-2, an explanatorynote (c-3) represents the result of Experimental Example 4-3, and anexplanatory note (c-4) represents the result of Experimental Example4-4.

As shown in FIGS. 10A and 10B, Experimental Example 4-1 using only theplate-like ceramic body and Experimental Example 4-2 in which sedumswere planted on the plate-like ceramic body had a larger evaporationamount of water per unit time than Experimental Example 4-4 in whichKorean lawn grass was planted. Moreover, Experimental Examples 4-1 and4-2 had a smaller evaporation amount of water per unit time thanExperimental Example 4-3 using artificial soil for greening.

From the above-described results, it may be assumed that the evaporationof water of Experimental Examples 4-1 and 4-2 is maintained longer thanthat of Experimental Example 4-3 and Experimental Examples 4-1 and 4-2have a high cooling effect by the evaporation of water compared toExperimental Example 4-4.

INDUSTRIAL APPLICABILITY

Since the present invention provides a porous ceramic sintered bodysuitable for plant growth and with a high cooling effect, the presentinvention is extremely useful to industrial applicability.

REFERENCE SIGNS LIST

-   -   1, 100, 110 PLATE-LIKE CERAMIC BODY    -   10 DENSE LAYER    -   14 PORE    -   20 FIRST NON-DENSE LAYER    -   30 SECOND NON-DENSE LAYER

1. A porous ceramic sintered body comprising a pore volume, which is thetotal volume of pores with a diameter of 3 nm to 360 μm, of 0.2 cm³/g orlarger and comprising a micropore volume ratio of 30% by volume or more,in which the micropore volume ratio equals to the total volume of poreswith a diameter equal to or greater than 0.01 μm and less than 1 μmdivided by the pore volume.
 2. The porous ceramic sintered bodyaccording to claim 1, wherein a median pore diameter of pores with adiameter of 3 nm to 360 μm is smaller than 40 μm.
 3. The porous ceramicsintered body according to claim 1, comprising a layer-like dense layerhaving a bulk specific gravity of 0.7 g/cm³ or more.
 4. The porousceramic sintered body according to claim 1, further comprising anon-dense layer having a bulk specific gravity of less than 0.7 g/cm³.5. The porous ceramic sintered body according to claim 4, wherein thenon-dense layer is provided on both surfaces of the dense layer.
 6. Theporous ceramic sintered body according to claim 1, used as a greeningbase material.